The underlying mechanisms by which groups of undifferentiated cells divide and differentiate into complex structures remains one of the most interesting and important problems yet to be fully understood in developmental genetics. We propose to exploit Arabidopsis floral meristems as a system for understanding basic concepts related to plant development, with a particular emphasis on genetic interactions among genes that influence meristem identity. One of these genes, APETALA1 (AP1) plays a pivotal role in this process since it is sufficient to signal plants to form flowers rather than shoots. The AP1 gene encodes a MADS-box transcription factor and is transcriptionally activated in young flower primordia when they initially arise on the flank of the inflorescence shoot meristem. We will use transgenic plants that ectopically express AP1 to investigate the interaction between AP1 and other meristem identity, organ identity, and flowering-time genes. Mutant screens will be performed on AP1 gain-of-function transgenic lines as well as on ap1 mutant alleles to identify and characterize other genetic loci that interact with AP1 to influence its activity. We will identify a cis-actihg element within the AP1 promoter that is sufficient to direct floral meristem-specific expression, and we will use this functionally defined element to clone the trans-acting factor(s) that mediates floral meristem activation of API transcription. Finally we will identify the consensus DNA target site to which the AP1 protein binds and we will isolate and characterize downstream genes regulated by AP1. The information gained from these studies will provide significant insights into the complex genetic interactions that occur during the establishment of floral meristems, and into general mechanisms by which the control of tissue-specific gene expression affects the developmental fate of groups of undifferentiated cells. In addition, these studies should provide the tools for manipulating flowering time in diverse plant species, which would have significant impact on agriculturally important crop plants.